Electroabsorption modulated lasers (EMLs) are known in the art primarily for digital applications. Such lasers typically include a multi-quantum well laser and a modulator formed in a body of InP. (See, eg, Johnson, et al., "High Speed Integrated Electroabsorption Modulators" SPIE Proceedings, Vol. 30-38, pp. 30-38 (Feb. 1997) and Aoki, et al., "Novel Structure MQW Electroabsorption Modulator IDFB Laser . . . " Electronics Letters, vol. 27, pp. 2138-2140 (Nov. 1991), which are incorporated by reference herein). The transfer function of such lasers, which is the light output as a function of voltage across the modulator, tends to be highly nonlinear. In particular, a sharp transfer function is exhibited, which is suitable for digital applications. However, analog applications normally require a linear transfer function.
In order to produce a more linear transfer function, it has been proposed to apply a predistortion to the input RF signal to the laser. This solution tends to be expensive and complex.
It is desirable, therefore, to provide a modulator which exhibits a fairly linear transfer function without the need for external circuitry.